Batch experiments: a tool to evaluate the fate of organic contaminants in MAR prefeasibility studies

Contaminants of emerging concern (CECs) present in runoff water pose significant risks to water quality. Understanding the processes that control their attenuation is thus crucial for effective mitigation strategies. The research is motivated by the pre-feasibility study of Managed Aquifer Recharge (MAR) in a Cretaceous Chalk Aquifer in the Hesbaye region (in Belgium), aiming to assess the suitability of runoff water as a potential source for recharge. Specifically, the study evaluates whether the natural filtration capacity of Hesbaye loamy soils can sufficiently reduce the contaminant load present in runoff water to meet water quality standards. In this context, sorption and biodegradability of per- and polyfluoroalkyl substances (PFASs), alkylphenols and benzotriazoles present in runoff water are investigated through controlled batch experiments. Three batch reactors were set up with a water/ soil volumetric ratio of 85:15 and were spiked with CECs at a concentration of 0.05 ppm. In each of these triplicates, synthetic water of similar chemical composition than the studied runoff water (major ions and DOC) was used. Three additional reactors were used as controls: one abiotic control to evaluate sorption of CECs on the soil, one biotic control for assessing their biotransformation, and the last one to assess the potential sorption of PFASs on the reactor glass bottles. Samples were collected daily the first week and then weekly from each reactors during 23 days and were analysed using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Results indicate variations in sorption capacities and degradation rates among different CECs, highlighting the complex nature of their interactions with soil and water matrices. Chemical modelling through PHREEQC allows the estimation of the sorption and biotransformation parameters for each studied chemical compound. These results will be beneficial for modelling the behaviour of runoff contaminants in the context of MAR systems.